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includes() JavaScript Array Method – How to Check If an Array Includes an Item

Whenever you use includes() on an array, the method does the following:

  1. It checks if the calling array includes the method's first argument.
  2. It returns true if the array includes the argument. Otherwise, it returns false.
note
  • A calling array is an array on which you used includes(). So, in bestColorsList.includes("white"), bestColorsList is the calling array.
  • includes() is sometimes written as Array.prototype.includes() because it is a method of the Array object's prototype property.

Syntax of the includes() Method​

includes() accepts two arguments. Here is the syntax:

callingArray.includes(valueToFind, startIndex);

Argument 1: valueToFind​

A valueToFind is the first argument accepted by the includes() method. It defines the value you wish to find in the calling array.

Example 1: Check if a given array includes "Tuesday"​

["Sunday", "Tuesday", "Friday"].includes("Tuesday");

// The invocation above will return: true

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Note that the includes() method is case-sensitive.

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Example 2: Check if a given array includes "SunDay"​

["Sunday", "Tuesday", "Friday"].includes("SunDay");

// The invocation above will return: false

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Example 3: Check if a given array includes 5​

[1, 3, 5, 7].includes(5);

// The invocation above will return: true

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Argument 2: startIndex​

The startIndex argument is optional. It specifies the index position where you want the computer to start searching for the valueToFind argument.

note

The startIndex argument's default value is 0. Therefore, if omitted, the search will begin at index 0.

Example 1: From the 3rd index position, check if a given array includes "Tuesday"​

const daysOfWeek = [
  "Sunday",
  "Tuesday",
  "Thursday",
  "Friday",
  "Tuesday",
  "Sunday",
  "Tuesday",
  "Friday",
];

daysOfWeek.includes("Tuesday", 3);

// The invocation above will return: true

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Example 2: From the 1st index position, check if a given array includes "Sunday"​

const daysOfWeek = [
  "Sunday",
  "Tuesday",
  "Friday",
  "Monday",
  "Tuesday",
  "Friday",
];

daysOfWeek.includes("Sunday", 1);

// The invocation above will return: false

Try it on StackBlitz

tip

Overview​

includes() checks if its calling array includes the method's first argument.

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